The present disclosure relates generally to gas turbine engines and more particularly to fuel injectors for use in combustors.
Gas turbine engines operate by passing a volume of high energy gases through a plurality of stages of vanes and blades, each having an airfoil, in order to drive turbines to produce rotational shaft power. The shaft power is used to drive a compressor to provide compressed air to a combustion process to generate the high energy gases. Additionally, the shaft power may be used to drive a fan or propeller to produce thrust for aircraft, to drive an electrical generator for powering aircraft systems, or to drive an electrical power plant in industrial gas turbine. In order to produce gases having sufficient energy to drive the turbines, it is necessary to combust the air at elevated temperatures and to compress the air to elevated pressures, which again increases the temperature. The combustion process involves injecting a stream of fuel into a high speed flow of compressed air within a combustion chamber. The fuel is typically finely atomized and swirled to ensure a high degree of mixing with the compressed air to produce a high fuel bum rate, such as is disclosed in U.S. Pat. No. 5,966,937 to Graves, which is assigned to United Technologies Corporation.
In order to atomize the fuel in the fuel injector, it is necessary to flow air through intricate passages and orifices within the injector to become entrained with the fuel. Flow of air over surfaces of the injector results in frictional heating of the injector. Heat from the air flow is passed to the fuel by conduction through the injector. As such, it is beneficial to insulate un-atomized fuel within the injector from the surfaces exposed to airflow. One method of insulating the fuel is to provide dead-air space within the injector, such as described in U.S. Pat. No. 6,715,292 to Hoke, which is assigned to United Technologies Corporation. Such spaces, however, are typically formed by interaction of two adjacent pieces of the injector, which requires precise machining of multiple components, careful matching of the components and sealing of the adjacent components. Such steps add significant time and expense to the manufacturing process. Further, the joints between the adjacent components reduce the efficiency of the insulation space. There is, therefore, a need for fuel injectors having improved insulating characteristics.